The kinetics of synthesis and turnover of nuclear RNA (primarily HnRNA) in sea urchin embryos will be studied. The relation of small RNA's (60-80 nucleotides) with extensive secondary structure to the turnover process is being examined. Kinetically, at least one class of these RNA's could be an intermediate in HnRNA turnover. More detailed kinetics, hybridization and structural studies of these small RNA's will be done. In addition, further attempts to isolate and characterize the nucleases involved in this turnover will be made. The kinetics of processing is being studied, primarily in pluteus embryos. Evidence for accumulation of processed non ribosomal RNA's in the size range of 12-23S will be confirmed. The rate of such processing will also be determined by kinetic studies and computer fitting of constants. BIBLIOGRAPHIC REFERENCES: A.I. Aronson and K. Chen (1977) Rates of RNA Chain Growth in Developing Sea Urchin Embryos. Develop. Biol., Aug., 1977, in press. A.I. Aronson (1977) Alteration of RNA metabolism in sea urchin embryos by an inhibitor of protein synthesis initiation. Biochem. Biophys. Acta., in press.